Temp - boiled down complicated/confusing topic

1. Dave Story
MBBS, MD, BMedSci, FANZCA
Professor and Chair of Anaesthesia
Head of Anaesthesia, Perioperative and Pain Medicine Unit (APPMU)
Melbourne Medical School
The University of Melbourne
The Meaning of Acidosis?

2. Conflict of Interest
I think I have no conflict of interest associated with this
presentation

3. The OED
Acid: from “acidus”, Latin: “sour” 1625
Boswell: “Rather an acid expression
of countenance”

4. Definitions of acid
Like other definitions “sour” is still used today
in parallel with other acid definitions
Depends on context

5. Strong ion acidosis- Stewart
Bicarbonate and hydrogen ions dependent factors
Bicarbonate is a marker not a mechanism
Base-excess is a marker
Sirker et al. Anaesthesia, 2002
Miller’s Anesthesia
H+ / HCO3
CO2
SID
Weak acids
Kw + Ka

6. Definitions of acid
Faraday, 1830s
English electrochemist,
-metal ions (sodium): base forming
-ions like chloride: acid forming

7. Definitions of acid
Arrhenius, 1870s
Swedish Chemist
• Electrolytic theory for ions
(Almost failed PhD but later Nobel Prize)
• First suggested CO2 greenhouse effect
General acid definition:
Substance that increases [H+]
when added to a solution

8. The next step
Naunyn, 1890s
German Diabetes physician
Combined Arrhenius definition of acid
with Faraday’s ideas:
plasma acid-base status partly determined by electrolytes
-particularly sodium and chloride

9. Henderson and Hasselbalch
Henderson, 1908
Boston Physician
H+ = Ka X [H2CO3]
[NaHCO3]
Henderson, Am J Phys, 1908
Hasselbalch, 1916
Danish gentleman farmer and chemist
pH = pKa + log [HCO3
-]
 pCO2
Astrup and Severinghaus,
The history of blood gasses, acids and bases. 1986

10. Van Slyke
US Clinical Chemist
1910 -1960s
“... the roles played…anions other than bicarbonate, and by
the cations, in determining the acid-base balance and the
bicarbonate content of the blood.”
Peters and Van Slyke,
Quantitative Clinical Chemistry 1935

11. Bicarbonate and carbon dioxide
Henderson and Hasselbalch (before 1920) knew challenge:
To assess effects of disease on bicarbonate,
must account for effects on carbon dioxide:
Isolate non-respiratory effects

12. The rise of bicarbonate
The Modern Way in 1950s
Calculate bicarbonate using Henderson-Hasselbalch equation:
Measure pH, pCO2 + know constants
pH = pKa + log [HCO3
-]
 pCO2
Carbonic acid true Bronstead-Lowry acid
Describe plasma pH ([H+]) with two measurable variables
Simple maths (B.C. - before calculators)
CO2 and bicarbonate = meaning of life, the universe, and everything
Christensen, Am J Med 1957

13. Intensive Care born 1952

14. Bicarbonate and carbon dioxide (again)
Siggaard-Andersen, Denmark, 1960s onward
Base Excess = amount of acid (mmol/l) added
to return blood to pH 7.40 after equilibration
with pCO2 of 40 mmHg at 37oC
Quantify change in non-respiratory component
www.osa.suite.dk

15. But…
Schwarz and Relman, NEJM 1963
Boston Physicians
Found flaws in (original) base-excess: ABE
CO2 and bicarb “rules-of-thumb”
and
“The Great Trans-Atlantic Acid-Base Debate”
Bunker, Anesthesiology, 1965

16. Then we have…
Siggaard-Andersen (fights back)
-Altered the “buffering” component
“Standard base-excess”
-Gained support form Severinghaus (US)
Severinghaus, Am J Respir Crit Care
Med, 1998

17. Peter Stewart 1921-1993
Canadian physiologist working in USA
Stewart. Can J Physiol Pharmacol 1983
Acid base chemistry:
“…piecemeal, qualitative, confusing…”
Returned to Arrhenius, Naunyn, Van Slyke
QUANTITATIVE
Used principles of chemistry:
electroneutrality
conservation of mass
dissociation of electrolytes

18. Strong ion acidosis- Stewart
Bicarbonate and hydrogen ions dependent factors
Bicarbonate is a marker not a mechanism
Base-excess is a marker
Sirker et al. Anaesthesia, 2002
Miller’s Anesthesia
H+ / HCO3
CO2
SID
Weak acids
Kw + Ka

19. The Gamblegram
Gamble , 1950s
- chloride = acid
- Gamblegram
- important aid to Stewart
Gamble,
Chemical Anatomy, Physiology
and Pathology of Extracellular Fluid 1954
Watson: www.ppn.med.sc.edu/watson/Acidbase/

20. Fencl
Boston based Physician
Originally suggested dividing
base-excess into effects of:
• Sodium
• Chloride
• Albumin
• Unmeasured ions
Gilfix J Crit Care 1993

21. Figge
Boston Physician
-quantified the base-excess effect of albumin
Complex version
Albumin effect (mmol/L) = (0.123pH- 0.631) X [42-albumin (g/l)].
Simple version:
Albumin effect (meq/L) = 0.25 X (42-Albumin)
Figge, Crit Care Med 1998
Value for anion gap increasingly understood
(even by Boston Physicians)
Fencl-Stewart = Figge-Fencl
www.acid-base.org

22. Kellum and the SIG
(NOT) Boston physician
Strong ion gap:
Sum of all measured strong ions,
and weak anions albumin, phosphate, bicarbonate
“anion-gap” on steroids
Kellum J Crit Care 1995
Net unmeasured ions
Lloyd, Crit Care Resus, 2005

23. Then I came along…
1. SBE = overall metabolic effect
2. Principal SID = Na – Cl (simplify Fencl), 140 – 102 = 38 (35)
3. Principal Weak acid = albumin (use simple Figge),
4. Rest = other ions
SBE = NaCl efffect + Albumin Effect + Other ion effect
For bedside use, not for the OCD
Not a Boston Physician

24. Simplify

25. In 2014 add lactate…
Plasma lactate now routinely measured
SBE =
NaCl Effect + Albumin Effect + Lactate Ion Effect + Other Ions
Lactate is a strong anion so effect on SBE = negative [lactate]
Median Reference Range = 1 mmol/L (ie when SBE = 0)
SBE effect = 1 – lactate, mmol/L
Eg Lactate ion effect of lactate of 4 mmol/L = - 3 mmol/L
Story, Anesthesia and Analgesia, 2006

26. SBE = NaCl + Albumin + Lactate + OI
78 yr old female with AAA post op
Na = 142, Cl = 110, Albumin = 26, Lactate = 6,
SBE = - 8 mmol/L
NaCl effect = 142 - 110 - 38 = - 6 mmol/l
Albumin effect = 0.25 x (42-26) = 0.25 x (16) = 4 mmol/l
Lactate effect = 1 - 6 mmol/L = -5 mmol/L
Other ions = SBE – NaCl effect – Albumin – Lactate
OI = -8 – (-6) - 4 – (-5)
= - 1 mmol/L

27. How will clinical acid-base evolve?
• Readily understood
• Clinically useful
• Quantifiable
• Identifiable
• Modifiable
Try different approaches in
YOUR clinical practice!
But, in my view…

28. Rules-of-thumb
The Neanderthals

29. Base-excess
The “sapiens”
way forward

30. But can the US cope?

31. …and add Stewart!
Thank you !!